In the integrated circuit industry, communication among multiple microprocessors or multiple integrated circuits is crucial. A bus protocol is usually used to efficiently interface one integrated circuit to other integrated circuits in an electrical system.
In some cases, a first integrated circuit within an electrical system may request or be required to enter and operate in a low-power mode of operation. In many cases, systems are designed so that once the first integrated circuit, usually by software command enters low-power mode, it does so automatically, ignoring its external electrical interfaces within a synchronized or protocol-based system environment. The problem with this type of system interfacing is that the entrance into the low-power mode of operation by the first integrated circuit may require special preprocessing, may require peripherals to be informed of the low-power mode or synchronized with the low-power mode, may not be timely and may need to be delayed by the system until a more appropriate time, etc. Due to the fact that the processor automatically entered the low-power mode, the system was not able to delay or better prepare for the low-power mode and system complications can occur. Other integrated circuits have an external integrated circuit pin specifically designed for informing an integrated circuit if a low-power mode can or cannot be entered when requested. Due to the fact that small integrated circuits are desired, the number of external pins on an integrated circuit should be kept at a minimum. Therefore, the adding of the extra external pin to control low-power mode entrance is not completely advantageous.